Multiple wavelength light emitting device, electronic apparatus, and interference mirror

ABSTRACT

A multiple wavelength light emitting device is provided wherewith the resonance strength and directivity between colors can be easily adjusted for balance. This light emitting device comprises a light emission means  4  for emitting light containing wavelength components to be output, and a semi-reflecting layer group  2  wherein semi-reflecting layers  2 R,  2 G, and  2 B that transmit some light having specific wavelengths emitted from the light emission means and reflect the remainder are stacked up in order in the direction of light advance in association with wavelengths of light to be output. Light emission regions A R , A G , and A B  are determined in association with the wavelengths of light to be output. The configuration is such that, in the light emission regions, the distances L R , L G  and L B  between a reflecting surface for fight from the light emission means side of the semi-reflecting layers  2 R,  2 G, and  2 B that reflect light output from those light emission regions and a point existing in an interval from the end of the light emitting layer on the semi-reflecting layer group side to the reflecting layer are adjusted so as to have an optical path length at which that light resonates.

This is one of two reissue applications of U.S. Pat. No. 6,791,261. Thefirst reissue is application Ser. No. 11/520,860, filed Sep. 14, 2006.The second reissue is this application. This application also is areissue divisional of Reissue application Ser. No. 11/520,860.

This invention relates to improvements in a light emitting devicecapable of emitting multiple colors suitable for application for examplein organic electro-luminescence(=EL) devices.

The art of combining a reflective layer with a multi-layer dielectricfilm wherein layers having differing refractive indexes are alternatelystacked, and therewith reflecting light of specific wavelengths isknown. In Shingaku Gihou, OME 94-79 (March, 1995), pp 7-12, the conceptis set forth of using very small resonance structures based on suchmulti-layer dielectric films to emit multiple light colors. According tothis literature, by adjusting the positions of the light emission layerand the reflective surface where reflection occurs in these very smallresonance structures, resonant light can be output having any of thewavelengths contained in the light output by the emission layers.

In Japanese Patent Laid-open No. 275381/1994, for example, a lightemitting device having the layer structure illustrated in FIG. 13 isdisclosed. This light emitting device comprises a transparent substrate100, a very small resonance structure 102, a positive electrode 103, ahole transport layer 106, an organic EL layer 104, and negativeelectrodes 105. The wavelengths are selected by altering each of thethicknesses of the positive electrodes 103.

In the article written by members of Bell laboratory, J. Appl. Phys.80(12), Dec. 15, 1996, a light emitting device having the layerstructure illustrated in FIG. 14 is disclosed. This light emittingdevice comprises a transparent substrate 100, a very small resonancestructure 102, SiO₂ film 108, a positive electrode 103, a hole transportlayer 106, an organic EL layer 104, and negative electrodes 105. Thethicknesses of the negative electrodes 103 are the same, but the opticalpath lengths are altered, respectively, by an SiO₂ layer, to select theresonant light wavelength.

With light emitting devices having the structure set forth in thepublicized literature noted above, however, there is a problem in thatit is very difficult to design light emitting devices optimized for allof a plurality of wavelengths. In other words, the very small resonancestructure and gap adjustment materials are optimized for a specificwavelength dispersion. Wherefore, with a very small resonance structuredesigned so that it is compatible with one of the plurality of lightcolors having a range of wavelengths, adequate reflectance cannot beachieved relative to other wavelength dispersions. In a color displayapparatus, for example, it is necessary to balance the resonanceintensity and color purity of each of the colors R (red), G (green), andB (blue) according to the characteristics of human vision. Suchbalancing adjustments are difficult with conventional light emittingdevices.

That having been said, it is nevertheless very difficult in actualmanufacturing practice to make the structure of the multi-layerdielectric film different for each pixel (light emission region) unit,therefor this is a difficult method to realise industrially, and hencean expensive process.

Thereupon, a first object of the present invention is to provide amultiple wavelength light emitting device that is balanced and optimizedfor a plurality of wavelengths.

A second object of the present invention is to provide a multiplewavelength light emitting device wherewith optimization for a pluralityof wavelengths is easy, and the manufacture thereof is easy.

A third object of the present invention is to provide an electronicapparatus capable of emitting light of a plurality of optimizedwavelengths.

A fourth object of the present invention is to provide an interferencemirror capable of sharpening and emitting a multiple wavelength lightspectrum.

An invention that realizes the first object noted above is a multiplewavelength light emitting device for emitting multiple light beamshaving differing wavelengths, comprising:

-   -   1) light emission means for emitting light containing the        wavelength components to be output;    -   2) a reflecting layer positioned in proximity to the light        emission means; and    -   3) a semi-reflecting layer group that is positioned so as to be        in opposition with the reflecting layer with the light emission        means sandwiched therebetween, wherein semi-reflecting layers        that reflect some of the light emitted from the light emission        means having specific wavelengths, while transmitting the        remainder, are stacked up in order in the direction of light        travel corresponding to the light wavelengths to be output.

The present invention is also a multiple wavelength light emittingdevice that comprises at least two but possibly more light emissionregions such that the wavelengths of the output light differ, structuredso that the distance between a reflecting surface for light from thelight emission means side on the semi-reflecting layers that reflectsome of the light output from one of the plurality of light emissionregions and a point that exists in the interval from the end of thelight emission means on the semi-reflecting layer group side to thereflecting layer is adjusted so that it becomes an optical path lengthat which light of the wavelength output from that light emission regionresonates.

Based on the structure described above, the semi-reflecting layer groupis optimized for all light wavelengths that are to be emitted, in any ofthe light emission regions. By adjusting the distance between thereflecting surface of the semi-reflecting layers for the light from thelight emission means side and the point existing in the interval fromthe end of the semi-reflecting layer group side of the light emissionmeans to the reflecting layer, and preferably the distance between thelight emission points within the light emission means and the surface(reflecting surface) on the light emission means side of the reflectinglayer, according to the light emission means and reflecting layer used,which optimized light is output is determined. The semi-reflectinglayers other than those optimized for light of wavelengths other thanthose output merely function commonly as semi-transparent layersexhibiting a certain attenuation factor, wherefore it is possible tomaintain balance between light of multiple wavelengths.

There is no limitation on the “light emission means,” as used here, butit is at least necessary that the wavelength component be generated forthe light that one wishes to output. The “reflective layer” should forma flat surface, but it does not necessarily have to have a uniform flatsurface. The language “in proximity to” includes cases where there iscontact with the light emission means, and cases where the positioningresults in a slight gap therebetween. So long as a reflective action isexhibited, this may be something that is not closely and indivisiblyconnected to the light emission means. The “light emission region” is adomain for outputting light having some wavelength dispersion, andsignifies that light of different wavelengths is output in each lightemission region. “Wavelength” is inclusive of a wide range ofwavelengths, including ultraviolet and infrared radiation in addition towavelengths in the visible light region. “Semi-reflecting layers”include structures such as half mirrors or polarizing panels in additionto interfering laminar structures wherein multiple film layers havingdifferent refractive indexes are stacked in layers. In the case of avery small dielectric-based resonating structure, “reflecting surface”refers to the surface on the side toward the light emission means.“Optical path length” corresponds to the product of the medium'srefractive index and thickness.

The specification of the “point existing in the interval from thesemi-reflecting layer group side of the light emission means to thesurface of the reflecting layer” is for the purpose of adjusting theposition in the thickness direction where resonance conditions will besatisfied by the light emission means configuration. Here, thepositional relationship in the thickness direction (light axis) isdefined, and a plane that emits light or reflects light (in the case ofa reflecting layer) is formed by the set of “points” that satisfy theresonance conditions in the light emission means overall. Here, when thepoint existing in the interval from the end of the light emission meanson the semi-reflecting layer group side to the reflecting layer is onthe reflecting surface of the reflecting layer, the distance L betweenthe reflecting surface on the light emission means side in thesemi-reflecting layer of the plurality of semi-reflecting layers thatreflects light of wavelength λ, in the light emission region whereinlight of wavelength λ is output, and the point existing in the intervalfrom the end of the semi-reflecting group side in the light emissionmeans to the surface of the reflecting layer is adjusted so as tosatisfy the relationshipL=Σdi  Eq. 1Σ(ni·di)+m₁·(Φ/2π)·λ=m₂·λ/2where ni is the refractive index of the i'th substance between thesemi-reflecting layer and the light emitting surface, di is thethickness thereof, Φ is the phase shift occurring at the reflectingsurface in the reflecting layer, and m₁ and m₂ are natural numbers. Lcorresponds to the actual distance, while Σ (ni·di) corresponds to theoptical path length. It is a necessary condition for resonance betweenthe semi-reflecting surface and the reflecting surface placed on theside opposite thereto that the sum of the optical path length and thephase shift be a natural multiple of the half-wavelength.

There are also cases where a resonance condition is set, setting thepoint in the interval from the end of the light emission means on thesemi-reflecting layer group side to the reflecting layer as the lightemission point in the light emission means. In such cases as this, thedistance L between the reflecting surface on the light emission meansside in the semi-reflecting layer of the plurality of semi-reflectinglayers that reflects light of wavelength λ, in the light emission regionwherein light of wavelength λ is output, and the point existing in theinterval from the end of the semi-reflecting group side in the lightemission means to the surface of the reflecting layer is adjusted so asto satisfy the relationshipL=Σdi  Eq. 2Σ(ni·di)=m₂·λ/2+(2m₃+1)·λ/4where ni is the refractive index of the i'th substance between thereflective surface and the point, di is the thickness thereof, m₂ is anatural number, and m₃ is an integer greater than 0.

The semi-reflecting layer group here is placed evenly so that multipletypes of semi-reflecting layers having differing wavelengthscorresponding to the plurality of light wavelengths are not separated bya light emission region. The reflecting surface for the light from thelight emission means side of the semi-reflecting layer in thesemi-reflecting layer group is in a different position in the thicknessdirection for each light emission region having a different lightemission wavelength.

It is to be preferred that the semi-reflecting layer group be arrangedso that the semi-reflecting layer reflecting light of longer wavelengthis on the side nearer to the light emitting device. This is because itis harder for light of short wavelength to be reflected by asemi-reflecting layer optimized for light of longer wavelength.

More specifically, the semi-reflecting layers making up thesemi-reflecting layer group are configured such that two layers ofdiffering refractive index are stacked up alternately. If we have twosemi-reflecting layers having different refractive indexes, for example,and take n1 as the refractive index of one layer, d1 as the thicknessthereof, n2 as the refractive index of the other layer, and d2 as thethickness thereof, then, when the wavelength of the light reflected inthat semi-reflecting layer is λ and m is made 0 or a natural number,then an adjustment is made to satisfy the relationshipn1·d1=n2·d2=(¼+m/2)·λ  Eq. 3This is an interference condition in this resonance structure. Itcorresponds to the half-wavelength in one combination of two layers.Reflection occurs when light from a layer of low refractive index isincident on a layer of high refractive index, wherefore it is desirablethat the arrangement be high refractive index) layer, low layer, highlayer, low layer, etc., stacking from the light emission means.

In the invention that realizes the second object noted above, thedistance from the reflecting surface for light from the light emissionmeans side of the semi-reflecting layer closest to the light emissionmeans to a point existing in the interval from the end of the lightemission means on the semi-reflecting layer group side to the reflectinglayer, and preferably the distance from the light emission point in thelight emission means and the surface on the light emission means side ofthe reflecting layer, according to light emission means and reflectinglayer used, are maintained at optical path lengths that satisfyEquations 1 and 2 above. And a gap adjustment layer is comprised,between the semi-reflecting layers, for adjusting the distance betweenthe reflecting surface for light from the light emission means side in asemi-reflecting layer other than the semi-reflecting layer closest tothe light emission means and the point existing in the interval from theend of the light emission means on the semi-reflecting layer group sideto the reflecting layer. The light emission means can be provided flat,without making the height thereof different in the thickness direction,wherefore the complex process of changing the layer thickness in eachlight emission region during manufacture can be omitted. The “gapadjustment means” need only exhibit light transmissivity, and may befreely selected from among resins or dielectric materials.

In the present invention, moreover, the distance from the reflectingsurface for light from the light emission means side of thesemi-reflecting layer closest to the light emission means to a pointexisting in the interval from the end of the light emission means on thesemi-reflecting layer group side to the reflecting layer, and preferablythe distance from the light emission point in the light emission meansand the surface on the light emission means side of the reflectinglayer, according to light emission means and reflecting layer used, aremaintained at lengths that satisfy Equations 1 and 2 above. And, inorder to adjust the distance between the reflecting surface for lightfrom the light emission means side in a semi-reflecting layer other thanthe semi-reflecting layer closest to the light emission means and thepoint existing in the interval from the end of the light emission meanson the semi-reflecting layer group side to the reflecting layer, thethickness of one layer, in the laminar structure configuring thesemi-reflecting layers wherein layers of different refractive index arestacked up, is altered. The gap is adjusted at the layer at the boundarywith the semi-reflecting layer, wherefore the quantity of materials usedcan be cut back, and it is only necessary, in terms of fabricationprocess, to control the film thickness when forming the layer thethickness thereof is to be adjusted, so the fabrication process can beomitted. It is preferable that the layer used for adjusting thethickness be the layer of high refractive index that is closest amongthe semi-reflecting layers to the light emission means.

In one aspect of the light emission means, multiple types of lightemission means that emit a relatively large number of light componentshaving wavelengths associated with light emission regions are providedso that they are associated with the light emission regions. Thisapplies to cases where optimal light emitting materials are used whichcontain the wavelength components for the light output in each lightemission region.

In another aspect of the light emission means, light emission means areprovided, common to each light emission region, capable of emittinglight including all components of wavelengths associated with the lightemission regions. If light emitting materials can be used which containall of the light wavelength components to be output, then there is noneed to prepare different light emitting material in each light emittingregion.

In concrete terms, the light emission means may comprise an organicelectro-luminescence layer sandwiched between electrode layers, whereinthe electrode provided at the back surface thereof corresponds to thereflection layer. In an organic electro-luminescence layer such as this,there are cases where the point where the electric field reaches maximumbetween the electrodes coincides with the light emission point in thelight emitting layer. It is preferable here that the light emissionmeans be provided with a hole transport layer on the side toward thepositive electrode. The light emission means may also be provided withan electron transport layer on the side of the organicelectro-luminescence layer toward the negative electrode.

When an organic electro-luminescence device is used, the distancebetween the reflecting surface for light from the light emission meansside of the semi-reflecting layers and a point existing in the intervalfrom the end of the light emission means on the semi-reflecting layerside to the reflecting layer is adjusted by the thickness of thepositive electrode located on the semi-reflecting layer group side ofthe light emission means.

When an organic electro-luminescence device is used, moreover, a layerfor adjusting the distance between the reflecting surface for light fromthe light emission means side of the semi-reflecting layers and a pointexisting in the interval from the end of the light emission means on thesemi-reflecting layer side to the reflecting layer (such as a holetransport layer) may be provided on the side of the light emission meanstoward the semi-reflecting layer group.

The negative electrode is configured of a material exhibiting lightreflectance. If some degree of light reflectance is exhibited, then itcan be used as a reflecting surface for the semi-reflecting layer.

When the configuration is made to enable light emission by the lightemission region, at least one or other of the electrode filmssandwiching the organic electro-luminescence layers is formed separatelyand independently in correspondence with the light emission region. Ifone or other of the electrode layers is separated, an active matrixdrive configuration is formed, whereas if both electrodes are separated,a passive matrix drive configuration is formed.

In terms of a concrete aspect, it is desirable that the electrodes beseparated by a partitioning material and, if necessary, that the organicelectro-luminescence layer also be partitioned off. Such a partitioningmaterial would consist of an insulator material.

In another possible aspect, of the electrode films, the negativeelectrode is made to correspond to the light emission region andseparated, while the positive electrode, in order to adjust the distancefrom the reflecting surface for light from the light emission means sideof the semi-reflecting layer closest to the light emission means to apoint existing in the interval from the end of the light emission meanson the semi-reflecting layer group side to the reflecting layer, has thethickness thereof changed and made to correspond to the light emissionregion.

In yet another possible aspect, of the electrode films, the positiveelectrode is made to correspond to the light emission region andseparated, and also, in order to adjust the distance from the reflectingsurface for light from the light emission means side of thesemi-reflecting layer closest to the light emission means to a pointexisting in the interval from the end of the light emission means on thesemi-reflecting layer group side to the reflecting layer, has thethickness thereof changed and made to correspond to the light emissionregion.

When such independent electrodes are provided, drive circuits areprovided separately for driving the electrically separated electrodefilms.

An invention that realizes the third object noted above is an electronicapparatus that is equipped with the multiple wavelength light emittingdevice of the present invention, as described in the foregoing. Onepossible concrete aspect thereof is an electronic apparatus thatfunctions as a display element, configured such that the light emissionregions in the multiple wavelength light emitting device are formed aspixels for displaying images, and such that the drive of each pixel canbe controlled in response to pixel information.

An invention that realizes the fourth object noted above is aninterference mirror, configured so as to be able to partially reflectlight of mutually differing wavelengths, and comprising a plurality ofinterference reflecting layers arrayed sequentially in the optical axisdirection, and gap adjustment layers positioned between the interferencereflecting layers.

Embodiments of the present invention will now be described by way offurther example only and with reference to the accompanying drawings; inwhich:

FIG. 1 is a cross-sectional diagram of the layer structure of a multiplewavelength light emitting device in a first embodiment of the presentinvention;

FIG. 2 is a diagram for explaining the interference conditions in asemi-reflecting layer;

FIG. 3 is a cross-sectional diagram of the layer structure of a multiplewavelength light emitting device in a second embodiment of the presentinvention;

FIG. 4 is a cross-sectional diagram of the layer structure of a multiplewavelength light emitting device in a third embodiment of the presentinvention;

FIG. 5 is a cross-sectional diagram of the layer structure of a multiplewavelength light emitting device in a fourth embodiment of the presentinvention;

FIG. 6 is a cross-sectional diagram of the layer structure of a multiplewavelength light emitting device in a fifth embodiment of the presentinvention;

FIG. 7 is a cross-sectional diagram of the layer structure of a multiplewavelength light emitting device in a sixth embodiment of the presentinvention;

FIG. 8 is a cross-sectional diagram of the layer structure of a multiplewavelength light emitting device in a seventh embodiment of the presentinvention;

FIG. 9 is a cross-sectional diagram of the layer structure of a multiplewavelength light emitting device in an eighth embodiment of the presentinvention;

FIG. 10 is a cross-sectional diagram of the layer structure of amultiple wavelength light emitting device in a ninth embodiment of thepresent invention;

FIG. 11 is a cross-sectional diagram of the layer structure of amultiple wavelength light emitting device in a tenth embodiment of thepresent invention;

FIG. 12 is a cross-sectional diagram of the layer structure of amultiple wavelength light emitting device in an eleventh embodiment ofthe present invention;

FIG. 13 is a cross-sectional diagram of the layer structure in apositive electrode gap adjustment type of light emitting device equippedwith a conventional single semi-reflecting layer; and

FIG. 14 is a cross-sectional diagram of the layer structure in adielectric gap adjustment type of light emitting device equipped with aconventional single semi-reflecting layer.

Embodiment 1

The first embodiment of the present invention pertains to a basicstructure in a case where three basic colors of light can be emitted, asnecessary for a color display, and gap adjustments are made with thepositive electrode. The layer structure of the multiple wavelength lightemitting device in the first embodiment is illustrated in FIG. 1. Thismultiple wavelength light emitting device, as depicted in FIG. 1,comprises a substrate 1, a semi-reflecting layer group 2, a positiveelectrode 3, a light emitting layer 4, and a negative electrode 5.

The substrate 1, which serves as the base during fabrication, is made ofa material that exhibits light transmissivity and certain mechanicalstrengths, and that can withstand heat treatment during fabrication.Such materials as glass, quartz, or resins are suitable for thissubstrate.

The semi-reflecting layer group 2 is configured by a stack ofsemi-reflecting layers 2R, 2G, and 2B, optimized for light of a certainwavelength. The semi-reflecting layer 2R is optimized to interfere witha red emitted light wavelength (in vicinity of 625 nm). Thesemi-reflecting layer 2G is optimized to interfere with a green emittedlight wavelength (in vicinity of 525 nm). And the semi-reflecting layer2B is optimized to interfere with a blue emitted light wavelength (invicinity of 450 nm). The semi-reflecting layers are arrayed with thesemi-reflecting layer 2R that resonates with light of longer wavelength(red) placed on the side closer to the light emitting layer 4, thesemi-reflecting layer 2G that resonates with light of a shorterwavelength (green) placed below that (lower down in FIG. 1), and withthe semi-reflecting layer 2B that resonates with light of the shortestwavelength (blue) placed below that. It is difficult for light of shortwavelength to be reflected by a semi-reflecting layer optimized forlight of a longer wavelength. Thus, by ordering the layers in this way,a more efficient light emitting device can be configured.

FIG. 2 is a diagram for explaining the interference conditions togetherwith an expanded view of the layer structure in the semi-reflectinglayers. Each semi-reflecting layer is configured as an alternate stackof two layers having different refractive index, namely a first layer 21and a second layer 22. In terms of the interference conditions asrelating to the refractive index and thickness, adjustments are made soas to satisfy the relationshipn1·d1=n2·d2=(¼+m/2)·λ  Eq. 3where n1 is the refractive index of the first layer 21, d1 is thethickness thereof, n2 is the refractive index of the second layer 22,and d2 is the thickness thereof. Also, λ is the wavelength of lightreflected in that semi-reflecting layer and m is an integer greater than0. This corresponds to the half-wavelength of light in one two-layercombination. Reflection occurs when light from a layer of low refractiveindex is incident in a layer of high refractive index. Therefore it isdesirable that the layers be stacked up, from the side toward the lightemission means, as a high (refractive index) layer, low layer, highlayer, low layer, etc.; set, in other words, so thatn1>n2

As to the specific materials used for the semi-reflecting layers 2R, 2G,and 2B, dielectric materials having differing refractive indexes arestacked up so as to satisfy the relationship represented in Equation 3.TiO₂ having a refractive index of 2.4 may be used for the first layer21, for example, and SiO₂ having a refractive index of 1.44 as thesecond layer 22. Alternatively, ZnS having a refractive index of 2.37may be used for the first layer 21, and MgF₂ having a refractive indexof 1.38 as the second layer 22. The layers configuring thesemi-reflecting layers are not limited to dielectric materials, however,and, for example, a laminar structure formed of resins or liquidcrystals, as disclosed in Japanese Patent Laid-open No. H10-133222/1998,may be employed. In the semi-reflecting layers, the thicknesses of thefirst and second layers are adjusted to agree with the wavelength inthat semi-reflecting layer. When the difference in refractive index issmall between the first and second layers, the reflectance will decline,wherefore many layers are stacked up.

The positive electrode 3 is provided so as to exhibit lighttransmissivity. The material of the positive electrode is used as thepositive electrode in an organic EL element, wherefore a metal, alloy,electrically conductive compound, or mixture thereof is used whichexhibits a large work function (4 eV or greater). ITO is a preferablechoice. If it is made thin to such degree that optical transmissivitycan be secured, then other materials such as gold metal, CuI, SnO₂, andZnO may be used. Here, the thickness of the positive electrode isadjusted for optical path length so that light resonates in each lightemission region and so that light transmissivity is exhibited. With theoptical path length, it is necessary to define two surfaces for causinglight to resonate. One surface is a reflecting surface for the lightfrom the light emitting layer side of the semi-reflecting layer thatpartially reflects light output from that light emission region. Theother surface is variously altered by the morphology of the lightemission means that contain the light emitting layer. Specifically, thissurface will either be a surface that is perpendicular to the light axisand contains a point in the interval from the end of the light emittinglayer on the semi-reflecting layer group side to the negative electrodesurface (this surface hereinafter expressed by the term “light emittingsurface”) or the reflecting surface on the negative electrode side. Ineach drawing, the position of the other surface is shown at theinterface between the negative electrode and light emitting layer.However, as noted above, these positions can be set in the interval fromthe surface of the light emitting layer (or hole transport layer incases where such is provided) on the semi-reflecting layer group side tothe negative electrode (reflecting layer). In the red light emissionregion A_(R), the distance L_(R) is adjusted so that the optical pathdistance between the boundary surface between the light emitting layer4R and negative electrode, and the reflecting surface of thesemi-reflecting layer 2R, satisfies the resonance conditions for redlight. In the green light emission region A_(G), the distance L_(G) isadjusted so that the optical path distance between the boundary surfacebetween the light emitting layer 4G and the negative electrode, and thereflecting surface of the semi-reflecting layer 2G, satisfies theresonance conditions for green light. And in the blue light emissionregion A_(B), the distance L_(b) is adjusted so that the optical pathdistance between the boundary surface between the light emitting layer4B and the negative electrode, and the reflecting surface of thesemi-reflecting layer 2B, satisfies the resonance conditions for greenlight.

Turning to the resonance conditions, as illustrated in FIG. 2, if λ istaken as the wavelength of the light that is output in that lightemission region, then the distance L between the interface between thelight emitting layer and the negative electrode, and the reflectingsurface for the light from the light emitting layer of thesemi-reflecting layer having a structure that reflects light of thatwavelength λ is adjusted so as to satisfy the relationshipL=Σdi  Eq. 1 (as above)Σ(ni·di)+m₁·(Φ/2π)·λ=m₂·λ2where ni is the refractive index of the i'th substance (including thedielectric layers in the semi-reflecting layers for other wavelengths)between the reflecting surface of that semi-reflecting layer and thelight emitting surface 40, di is the thickness thereof, and m₁ and m₂are natural numbers. When reflection is caused at the negative electrodesurface, the phase shift that develops during reflection at thereflecting surface is given as Φ. Red light in the light emission regionA_(R) does not pass through the other semi-reflecting layer or layersalong the way, wherefore adjustments are made so that the value of theproduct of the thickness and refractive index of the positive electrode3 becomes a natural multiple of the half-wavelength.

As to the resonance conditions, as described in the foregoing, when alight emitting surface is set with one point in the light emittinglayers 4R, 4G, and 4B as the light emission point, the distances L(L_(R), L_(G), L_(B)) between the reflecting surface on the lightemitting layer side in the semi-reflecting layers 2R, 2G, and 2B thatreflect light of wavelength λ and a point existing in interval from theend of the semi-reflecting layer side in the light emitting layers 4R,4G, and 4B to the reflecting layer (that is, the interface between thelight emitting layer 4 and negative electrode 5) is adjusted so as tosatisfy the relationshipL=Σdi  Eq. 2 (as above)Σ(ni·di)=m₂·λ/2+(2m₃+1)·λ/4where ni is the refractive index of the i'th substance between thereflecting surface and the point, di is the thickness thereof, m₂ is anatural number, and m₃ is an integer greater than 0.

The light emitting layers 4R, 4G, and 4B are formed, respectively, oforganic EL materials. The organic EL materials used emit lightcontaining a relatively high amount of light components of wavelengthsassociated with the light emission regions. The light emitting surfacechanges depending on whether or not a charge transport layer exists, aswill be described in conjunction with a subsequent embodiment. Thethickness of each light emitting layer is determined according to therelationship between the negative electrode that is the reflectingsurface and the light emission wavelength. For the material of the lightemitting layer it is possible to employ materials being researched anddeveloped as organic electro-luminescence device materials, such asthose set forth in Japanese Patent Laid-open No. 163967/1998 andJapanese Patent Laid-open No. 248276/1996. Specifically, the materialsused for the red light emitting layer 4R include cyanopolyphenylenevinyline precursor,2-1,3′,4′-dihydroxyphenyl-3,5,7-trihydroxy-1-benzopolyriumperchlorate,or PVK doped with DCM1. The materials used for the green light emittinglayer 4G include polyphenylene vinyline precursor,2,3,6,7-tetrahydro-11-oxo-1H,5H,11H-(1)penzopyrano6,7,8-ij-quinolidine-10-carbonate,and PVK doped with quotamine 6. And the materials used for the bluelight emitting layer 4B include aluminum quinolinol complex, pyrozolinedimer, 2,3,6,7-tetrahydro-9-methyl-11-oxo1H,5H,11H-(1)penzopyrano6,7,8-ij-quinolidine, distyro derivative, and PVK doped with1,1,4,4-triphenyl-1,3-butadiene.

The negative electrode 5 functions as the negative electrode of theorganic EL element, so a metal, alloy, electrically conductive compound,or mixture thereof having a small work function (4 eV or below) is used.It is particularly desirable, in the interest of enhancing theefficiency of the light emitting layer and causing the light to stronglyresonate, that a material of high reflectance be used. Specifically,such substances include diamond, aluminum nitride, boron nitride,sodium, sodium-potassium alloys, magnesium, lithium, magnesium-coppermixtures, magnesium-silver mixtures, magnesium-aluminum mixtures,magnesium-indium mixtures, aluminum-aluminum oxide mixtures, indium,lithium-aluminum mixtures, and rare earth metals lithiumfluride-aluminum, ie add flurides with A1 as either bilayer or Alloy.

In the configuration described above, when a certain voltage is appliedacross the positive electrode 3 and negative electrode 5, current flowsto the light emitting layers, inducing an electro-luminescence effect,whereupon light containing wavelength components in the spectrum definedby the light emitting material is emitted on both sides of the layer.The light emitted on the side of the negative electrode 5 is reflected,interferes either with the direct light from the light emitting surfaceor with the light reflected on the negative electrode side, and isejected to the ejection side (downward in FIG. 1). At this time, thereis a refractive index differential in the dielectric layers configuringthe semi-reflecting layer, wherefore reflection occurs at the interfaceof the dielectric layers having different refractive indexes. Accordingto the interference conditions of Equation 3 exhibited by the dielectriclayers, there is either a mutual canceling or mutual reinforcing effect,and only that light having the wavelength optimized in the dielectricmaterial is reflected with high efficiency. This interferes with thelight from the light emitting layer side, that is, with the lightreflected by the negative electrode surface and the direct light fromthe light emitting layer, and only light having a wavelength thatcoincides with the resonance conditions expressed above in Equation 1 or2, for example, resonates between the reflecting surface and the lightemitting surface. As to the light having other wavelength components,when light from the light emitting layer is incident on thesemi-reflecting layer corresponding to those wavelength components, thephase does not match and resonance does not occur, wherefore such lightis relatively weakened. As a consequence, that wavelength spectrum issharpened, and high-intensity light passes through the semi-reflectinglayer and is ejected. The other semi-reflecting layers that do not matchthe resonance conditions function merely as semitransparent films, andthe light attenuation and other effects resulting thereby are roughlythe same in every wavelength domain. For this reason, light of aplurality of wavelengths, balanced in terms of intensity and colorpurity, will be output from each light emission region.

As based on the first embodiment described in the foregoing, resonancestructures for each of three basic colors are stacked up, and resonanceconditions are determined by adjusting the distance between thereflecting surface for light from the light emission means side of thesemi-reflecting layers to a point existing in the interval from the endof the light emitting layer on the semi-reflecting layer side to thereflecting layer, wherefore it is possible to eject balanced light of aplurality of wavelengths.

As based on this embodiment, moreover, a semi-reflecting layer optimizedfor longer wavelengths is provided on the light emitting layer side,wherefore light can be emitted without affecting the light of otherwavelengths.

As based on this embodiment, furthermore, an organic EL element isadopted as the light emission means, making it possible to select amaterial having suitable wavelength dispersion from among many differentmaterials.

As based on this embodiment, moreover, the light emitting material ischanged in light emission wavelength units, wherefore light of higherpurity and intensity can be output.

As based on this embodiment, furthermore, the negative electrode isformed of a light-reflecting material, thus making it possible to effectresonance efficiently.

Embodiment 2

A second embodiment of the present invention pertains to a configurationwherein a hole transport layer is provided in the organic EL element ofthe first embodiment. In FIG. 3 is illustrated the layer structure ofthe multiple wavelength light emitting device of the second embodiment.This multiple wavelength light emitting device, as illustrated in FIG.3, comprises a substrate 1, a semi-reflecting layer group 2, a positiveelectrode 3, a hole transport layer 6, a light emitting layer 4, and anegative electrode 5.

The hole transport layer 6, also called a hole injection layer, is madeof an organic or inorganic material exhibiting either a hole injectionfunction or an electron barrier-forming function. Materials disclosed inJapanese Patent Laid-open No. 163967/1988 or Japanese Patent Laid-openNo. 248276/1996, for example, may be used. More specifically, thesubstances that may be used include triazole derivatives, oxadiazolederivatives, polyaryl alcane derivatives, pyrazoline derivatives,pyrazolone derivatives, phenylene diamine derivatives, arylaminederivatives, amino-substitution chalcone derivatives, oxazolederivatives, styrylanthracene derivatives, fluoronolene derivatives,hydrazone derivatives, stilbene derivatives, silazane derivatives,polysilane copolymers, aniline copolymers, and electrically conductivecomplex oligomers. The thickness thereof is made just sufficient tosupport the hole carrier function. However, when a hole transport layeris used, it is possible for the light emitting surface to be close tothe interface between the hole transport layer 6 and the light emittinglayer 4. Accordingly, in the interest of efficient light emission,thickness conditions are set for the light emitting layer and the holetransport layer such that mutual cancellation will not result fromreflection by the negative electrode 5.

Other than this, the layer structure is the same as in the firstembodiment and no further description is made here. When providing thehole transport layer, depending on the materials used in the lightemitting layer and hole transport layer, the thicknesses thereof areadjusted so as to optimally obtain the desired wavelengthcharacteristics.

As based on the second embodiment, in addition to realizing the samebenefits as with the first embodiment, the addition of the holetransport layer enables the light emission efficiency of the organic ELelement to be enhanced, resulting in an even brighter light emittingdevice.

Embodiment 3

A third embodiment pertains to a configuration wherein an electrontransport layer is provided in the organic EL element in the secondembodiment. The layer structure of the multiple wavelength lightemitting device in the third embodiment is illustrated in FIG. 4. Asillustrated in FIG. 4, a substrate 1, a semi-reflecting layer group 2, apositive electrode 3, a hole transport layer 6, a light emitting layer4, an electron transport layer 7, and a negative electrode 5 areprovided.

The electron transport layer, also called an electron injection layer,has a function whereby it takes electrons injected from the negativeelectrode and conveys them efficiently to the light emitting layer.Materials disclosed in Japanese Patent Laid-open No. 163967/1988,Japanese Patent Laid-open No. 248276/1996 or Japanese Patent Laid-openNo. 194393, for example, may be used. More specifically, the substancesthat may be used include nitro-substitution fluorolene derivatives,anthraquinodimethane derivatives, diphenylquinone derivatives, thiophandioxide derivatives, naphthalene perilene and other heterocyclictetracarbonate anhydrides, carbodiimide, freolenidine methanderivatives, anthraquinodimethanne and anthrolone derivatives,oxadiazole derivatives, and quinoxaline derivatives. The thicknessthereof is made just sufficient to support the electron carrierfunction.

In other respects the layer structure is the same as in the secondembodiment described above, so no further description is given here.However, the hole transport layer may be provided, or omitted, with thedecision as to whether to provide it or not being based on a balancewith the organic EL material.

As based on this third embodiment, in addition to realizing the samebenefits as with the second embodiment described earlier, the additionof the electron transport layer enables the light emission efficiency ofthe organic EL element to be enhanced, resulting in an even brighterlight emitting device.

Embodiment 4

A fourth embodiment of the present invention pertains to a configurationwherein the adjustment of the optical path length that is a resonancecondition in the organic EL element in the first embodiment is performedwith insulators. In FIG. 5 is illustrated the layer structure of themultiple wavelength light emitting device in the fourth embodiment. Thismultiple wavelength light emitting device, as illustrated in FIG. 5,comprises a substrate 1, a semi-reflecting 2, a positive electrode 3,insulators 8G and 8B, a light emitting layer 4, and a negative electrode5.

In this fourth embodiment, the positive electrode 3 is matched with theresonance conditions in the red light emission region A_(R) and formedin the same thickness in the other light emission regions also. On theother hand, however, in the green light emission region A_(G) and theblue light emission region A_(B), respectively, insulators 8G and 8B areprovided, in different thicknesses, so as to satisfy the resonanceconditions in Equations 1 and 2. However, in this embodiment, all thathas been done is to adjust the optical path length in order to causeresonance in the green and blue light emission regions, and an insulatormay be placed in the red domain. The insulators 8G and 8B may be made ofan organic or inorganic substance exhibiting light transmissivity. Adielectric such as SiO₂, Si₃N₄, or TiO₂ may be used, for example.However, there is a difference in refractive index between thedielectric and the positive electrode, wherefore the distances L_(G) andL_(B) from the semi-reflecting layers 2G and 2B to the light emittingsurface will differ slightly from the first embodiment. In otherrespects the layer structure is the same as in the embodiments describedearlier. When the charge carrier capability in the light emitting layeris low, moreover, a hole transport layer or an electron transport layer,or both, may be provided as in the second and third embodiments.

As based on this fourth embodiment, in addition to realizing the samebenefits as in the embodiments described earlier, since the positiveelectrode can be formed with a uniform thickness, light emitting devicescan be provided which are easier to fabricate when using a positiveelectrode material wherewith it is difficult to impart thicknessdifferences.

Embodiment 5

In the embodiments described above, a different light emitting layer isprovided in each light emission region. In a fifth embodiment of thepresent invention, however, the same light emitting layer is providedfor all of the light emission regions. In FIG. 6 is illustrated thelayer structure of the multiple wavelength light emitting device in thefifth embodiment. This multiple wavelength light emitting device, asillustrated in FIG. 6, comprises a substrate 1, semi-reflecting layergroup 2, positive electrode 3, light emitting layer 4, and negativeelectrode 5.

In this embodiment, the light emitting layer 4 is provided commonly forall of the light emitting layers. It is desirable that the lightemitting layer be made of a wide-band light emitting material containingin good balance the wavelength components of the light supplied from thelight emission regions in an intensity more than the predeterminedlevel. The materials which may be used for this purpose include, forexample, aluminum chelate (Alq₃) and polyparaphenylene vinyline. Thedistance between the reflecting surface of the semi-reflecting layer andthe light emitting surface is considered to be the same as in the firstembodiment. When the charge carrier capability in the light emittinglayer is low, moreover, a hole transport layer or an electron transportlayer, or both, may be provided as in the second and third embodiments.It is also permissible to adjust the optical path length with insulatorsas in the fourth embodiment. A diamine derivative (TAD) might be usedfor the hole transport layer used together with Alq₃.

In this configuration, light containing all of the wavelength componentsto be output is ejected from the light emitting layer 4. For thisreason, in any of the semi-reflecting layers, light having a wavelengthoptimized for that reflecting layer will be reflected. However, thedistance between the reflecting surface of the semi-reflecting layer andeither the light emission point (light emitting surface) in the lightemitting layer or the reflecting surface of the negative electrode isoptimized so as to match the resonance conditions for a wavelengthassociated with each light emission region, wherefore only light havinga wavelength within those resonance conditions is ejected with asharpened spectrum.

As based on this fifth embodiment, in addition to realizing the samebenefits as with the other embodiments, there is no need to fabricate alight emitting layer separately for each light emission region,wherefore manufacture is simplified.

Embodiment 6

In the embodiments described in the foregoing, different resonanceconditions are set for each light emission region with the positiveelectrode or insulators. In a sixth embodiment, however, the resonanceconditions are altered while keeping the thickness of every layeruniform. In FIG. 7 is illustrated the layer structure of the multiplewavelength light emitting device of this sixth embodiment. This multiplewavelength light emitting device, as illustrated in FIG. 7, comprises asubstrate 1, a semi-reflecting layer group 2 provided with spacers 9Gand 9B, a positive electrode 3, a light emitting layer 4, and a negativeelectrode 5.

The spacers 9G and 9B are layers provided for adjusting the gaps betweenthe semi-reflecting layers. These spacers should be made of a materialsuch as a resin or dielectric that exhibits high light transmissivityand that bonds well with the semi-reflecting layers. If it is possibleto maintain the distance between the semi-reflecting layers, needless tosay, these layers may be configured of a gas, a liquid, or a liquidcrystal, etc. The spacers 9G and 9B may be made of different materialshaving different refractive indexes. The materials for the lightemitting layers are selected so that in the light emitting layer 2R inthe red light emission region A_(R) more red light wavelength componentsare present, so that in the light emitting layer 2G in the green lightemission region A_(G) more green light wavelength components arepresent, so that in the light emitting layer 2B in the blue lightemission region A_(B) more blue light wavelength components are present,and so that comparatively few other wavelength components are present.In this embodiment, the layer structure is the same in every lightemission region, it being necessary to define the light emittingwavelength by the characteristics of the light emitting layer itself. Interms of resonance conditions, all of the light emission regions are setat uniform thickness with the positive electrode 5. That is, the opticalpath length between the light emitting surface of the light emittinglayer 4R and the reflecting surface in the semi-reflecting layer 2R thatis closest to the light emitting layer is maintained so as to correspondto a natural number multiple of the half-wavelength of the light (redlight) reflected in that semi-reflecting layer. The thicknesses of thespacers 9G and 9B are adjusted so that the optical path length betweenthe reflecting surface in the semi-reflecting layer 9G or 9B and thelight emitting surface of the light emission means satisfies theresonance conditions expressed in Equation 2. More specifically, for thegreen light emission region A_(g), an optical path length correspondingto the product of the refractive index n_(9G) and the thickness d_(9G)of the spacer 9G is added to Equation 2, and material having arefractive index so as to satisfy the resonance conditions is selectedand the thickness set. And for the blue light emission region A_(B), theoptical path length (n_(9G)·d_(9G)+n_(9B)·d_(9B)) for both the spacer 9Band the spacer 9G is added to Equation 2, and material having arefractive index so as to satisfy the resonance conditions is selectedand the thickness set. When the charge carrier capability in the lightemitting layer is low, moreover, a hole transport layer or an electrontransport layer, or both, may be provided as in the second and thirdembodiments.

In the configuration described in the foregoing, when light is ejectedfrom the light emitting layer, for the red light semi-reflecting layer2R closest to the light emitting layer, resonance and light emissionoccurs as in the first embodiment. For the other light emission regionsalso, since the optical path length thereof is adjusted so as tocoincide with a natural number multiple of the half-wavelength,resonance occurs, and a sharpened spectrum of the resonant wavelength isoutput.

As based on this sixth embodiment, in addition to realizing the samebenefits as in the other embodiments, the layers inclusive of thepositive electrode and light emitting layer may all be formed flat andof uniform thickness, wherefore such complex process steps as patterningcan be omitted and, hence, manufacturing costs reduced.

Embodiment 7

A seventh embodiment pertains to a modification of the gap adjustmentmethod employed in the sixth embodiment. In FIG. 8 is illustrated thelayer structure of the multiple wavelength light emitting device in thisseventh embodiment. This multiple wavelength light emitting device, asillustrated in FIG. 8, comprises a substrate 1, a semi-reflecting layergroup 2 equipped with gap adjustment layers 21G and 21B, a positiveelectrode 3, a light emitting layer 4, and a negative electrode 5.

The gap adjustment layer 21G is a layer for adjusting the gap betweenthe semi-reflecting layers, altering the thickness of the first layer 21that is the closest to the light emitting layer of the greensemi-reflecting layers 2G. The gap adjustment layer 21B is a layer foradjusting the gap between the semi-reflecting layers, altering thethickness of the first layer 21 that is closest to the light emittinglayer of the blue semi-reflecting layers 2B. Because the layersconfiguring the semi-reflecting layers are themselves dielectricmaterials, when the thickness of one layer is made different, that layerceases to be a layer that produces interference, and, with therefractive index and thickness thereof, it will contribute to anincrease in the optical path length given. More specifically, withrespect to the green light emission region A_(G), an optical path lengthcorresponding to the product of the refractive index n1 and thicknessd_(21G) of the gap adjustment layer 21G is added to Equation 2, andmaterial having a refractive index that satisfies the resonanceconditions is selected and its thickness set. With respect to the lightemission region A_(B), an optical path length n1·(d_(21G)+d_(21B)) forboth of the gap adjustment layers 21B and 21G is added to Equation 2,and material having a refractive index that satisfies the resonanceconditions is selected and its thickness set.

In other respects the configuration is the same as in the sixthembodiment.

As based on this seventh embodiment, the gap is adjusted with the layerat the interface with the semi-reflecting layer, wherefore savings inmaterials used can be realized, and, when forming the gap adjustmentlayer in the process of fabricating the semi-reflecting layers, it isonly necessary to control the film thickness, thus making it possible toreduce the number of manufacturing steps.

Embodiment 8

An eighth embodiment pertains to a structure wherewith it is possible tomake a light emitting layer emit light in each light emission region.The layer structure of the multiple wavelength light emitting device inthis eighth embodiment is illustrated in FIG. 9. This multiplewavelength light emitting device, as illustrated in FIG. 9, comprises asubstrate 1, a semi-reflecting layer group 2, a positive electrode 3, alight emitting layer 4, an electrically divided negative electrode 5, asubstrate 11, and banks 10. Also provided are drive circuits (not shown)for separately and independently applying control voltages V_(R), V_(G),and V_(B), to the electrodes 5R, 5G, and 5B that are electricallyseparated by the banks 10, together with interconnecting wiringtherefor.

In this embodiment, the banks 10 are provided at the interfaces of thelight emission regions, with negative electrodes formed so that they areelectrically separated in the domains partitioned by the banks. Thesubstrate 11 is also provided for forming the banks 10 and the negativeelectrode patterns. A suitable material for the banks 10 would bepolyimide, for example, or another organic or inorganic substance thatis an insulator and that can be patterned and formed with a fixed heightmatched with the light emission region. In addition to electricallyseparating the negative electrode, as illustrated, the banks may also beformed so that they electrically separate the light emitting layertogether with the negative electrode. When configured thusly, the layerstructure corresponding to the organic EL element is sequentially formedon the base provided by the substrate 11. The substrate 11 need onlyexhibit mechanical strength and thermal strength. The drive circuits maybe configured with TFTs, etc., so that they can drive each lightemission region. Since the positive electrode is a common substrate, itforms an active matrix type of drive scheme. When the charge carriercapability in the light emitting layer is low, moreover, a holetransport layer or an electron transport layer, or both, may be providedas in the second and third embodiments. The positive electrode may alsocomprise a structure wherein insulators are stacked, as indicated in thefourth embodiment. The light emitting layers may all be providedcommonly also, as in the fifth embodiment.

In the configuration described in the foregoing, when drive voltagesV_(R), V_(G), and V_(B) are applied so as to control the drive circuitsin each light emission region, current flows only in the correspondinglight emitting layer, and only the hue of that light emission region isoutput. If the light emission regions are formed so that they areassociated with color pixels in a color display apparatus, and the drivevoltage in each light emission region controlled with a correspondenceestablished with RGB signals in color image data, the whole willfunction as a color display apparatus. In addition, the configuration issuch as to permit the light emission color to be freely altered evenwhen used as a light emitting device.

As based on the eighth embodiment described in the foregoing, theconfiguration is made so that the negative electrode is electricallyseparated into units that can be driven separately. Thus, in addition torealizing the benefits provided by the other embodiments, it is possibleto make the multiple wavelength light emitting device of the presentinvention function as a display apparatus or other electronic apparatus.

Embodiment 9

A ninth embodiment pertains to a modification of the eighth embodimentwherein the negative electrode is separated by patterning. The layerstructure of the multiple wavelength light emitting device in this ninthembodiment is illustrated in FIG. 10. This multiple wavelength lightemitting device, as illustrated in FIG. 10, comprises a substrate 1, asemi-reflecting layer group 2, a positive electrode 3, a light emittinglayer 4, a patterned negative electrode 5, and a substrate 11. Alsoprovided are drive circuits (not shown) for separately and independentlyapplying control voltages V_(R), V_(G), and V_(B), to the electricallyseparated negative electrodes 5R, 5G, and 5B, together withinterconnecting wiring therefor.

In this embodiment, the negative electrode 5 is patterned in associationwith the light emission regions. The light emitting layer 4 is providedcommonly for all of the light emission regions, as described inconjunction with the fourth embodiment. The material for the lightemitting layer is the same as in the fourth embodiment. The substrate 11is necessary when configuring the negative electrode by patterning sothat it is electrically separated. In this embodiment also it ispreferable that fabrication begin from the substrate 11. The drivecircuits can separately and independently drive the electricallyseparated negative electrodes 5R, 5G, and 5B. In other respects theconfiguration is the same as in the first embodiment. If the positiveelectrode 3 is also patterned, and fashioned so as to configure thenegative electrode 5 and matrix wiring, then this light emitting devicecan be driven as a passive matrix type of display apparatus.

In this configuration, when drive voltages V_(R), V_(G), and V_(B) areapplied to control the drive circuits for each light emitting domain,current flows only in the corresponding light emitting layer, and onlythe hue of that light emission region is output. If the light emissionregions are formed so that they are associated with color pixels in acolor display apparatus, and the drive voltage in each light emissionregion controlled with a correspondence established with RGB signals incolor image data, the whole will function as a color display apparatus.In addition, the configuration is such as to permit the light emissioncolor to be freely altered even when used as a light emitting device.

As based on the ninth embodiment described in the foregoing, theconfiguration is made so that the negative electrode is electricallyseparated into units that can be driven separately. Thus, in addition torealizing the benefits provided by the other embodiments, it is possibleto provide a multiple wavelength light emitting device having acomparatively simple layer structure that can be easily fabricated.

Embodiment 10

A tenth embodiment pertains to a configuration wherein, contrary to theeighth embodiment, the positive electrode is separated by banks. Thelayer structure of the multiple wavelength light emitting device in thistenth embodiment is illustrated in FIG. 11. This multiple wavelengthlight emitting device, as illustrated in FIG. 11, comprises a substrate1, a semi-reflecting layer group 2, a positive electrode 3 separated bybanks 10, a light emitting layer 4, a negative electrode 5, and asubstrate 11. Also provided are drive circuits (not shown) forseparately and independently applying control voltages V_(R), V_(G), andV_(B), to the electrically separated positive electrodes 3R, 3G, and 3B,together with interconnecting wiring therefor.

In this embodiment, banks 10 are provided so that they can separate thelight emitting layer and the positive electrode in each light emittingdomain. The same materials and formation method can be used for thebanks 10 and the substrate 11 as set forth in conjunction with theeighth embodiment. It is particularly desirable that the ink jet methodset forth in Japanese Patent Laid-open No. H10-153967/1998 be used asthe fabrication method for forming the banks on the substrate andpattern-forming the electrodes and light emitting layer. As to the drivescheme, when the negative electrode 5 is made a common electrode as inthis embodiment, it is possible to provide a TFT on the side of thepositive electrode 3, thereby permitting operation as an active matrixdrive scheme. Also, by electrically separating the negative electrodeside also, using banks and patterning, and forming a matrix-formelectrode structure above and below the light emitting layer, it ispossible to effect operation as a simple matrix drive scheme.

When the charge carrier capability in the light emitting layer is low,moreover, a hole transport layer or an electron transport layer, orboth, may be provided as in the second and third embodiments, Thepositive electrode may also comprise a structure wherein insulators arestacked, as indicated in the fourth embodiment. The light emittinglayers may all be provided commonly also, as in the fifth embodiment.

In this configuration, when drive voltages V_(R), V_(G), and V_(B) areapplied to control the drive circuits for each light emitting domain,current flows only in the corresponding light emitting layer, and onlythe hue of that light emission region is output. If the light emissionregions are formed so that they are associated with color pixels in acolor display apparatus, and the drive voltage in each light emissionregion controlled with a correspondence established with RGB signals incolor image data, the whole will function as a color display apparatus.In addition, the configuration is such as to permit the light emissioncolor to be freely altered even when used as a simple light emittingdevice.

As based on the tenth embodiment described in the foregoing, theconfiguration is made so that the positive electrode is electricallyseparated into units that can be driven separately. Thus, in addition torealizing the benefits provided by the other embodiments, it is possibleto make the multiple wavelength light emitting device of the presentinvention function as a display apparatus or other electronic apparatus.

Embodiment 11

An eleventh embodiment pertains to a modification of the tenthembodiment wherein the positive electrode is separated by patterning.The layer structure of the multiple wavelength light emitting device inthis eleventh embodiment is illustrated in FIG. 12. This multiplewavelength light emitting device, as illustrated in FIG. 12, comprises asubstrate 1, a semi-reflecting layer group 2, a patterned positiveelectrode 3, a light emitting layer 4, a negative electrode 5, and asubstrate 11. Also provided are drive circuits (not shown) forseparately and independently applying control voltages V_(R), V_(G), andV_(B), to the electrically separated positive electrodes 3R, 3G, and 3B,together with interconnecting wiring therefor.

In this embodiment, the positive electrode 3 is patterned in associationwith the light emitting domains. The polarity of the drive circuits isopposite to the polarity in the eighth and ninth embodiments describedearlier. The drive circuits, moreover, are fashioned so that they canindividually and independently drive the electrically separated positiveelectrodes 3R, 3G, and 3B. In other respects, the configuration is thesame as that of the eighth embodiment. In this embodiment, because thenegative electrode side is not formed so as to be separate andindependent, it is possible to form the laminar structure from the sideof the semi-reflecting layer group 2. When forming the positiveelectrode 3, it is only necessary to perform patterning coordinated withthe light emitting domains.

In this configuration, when drive voltages V_(R), V_(G), and V_(B) areapplied to control the drive circuits for each light emitting domain,current flows only in the corresponding light emitting layer, and onlythe hue of that light emission region is output. If the light emissionregions are formed so that they are associated with color pixels in acolor display apparatus, and the drive voltage in each light emissionregion controlled with a correspondence established with RGB signals incolor image data, the whole will function as a color display apparatus.In addition, the configuration is such as to permit the light emissioncolor to be freely altered even when used as a simple light emittingdevice.

As based on the eleventh embodiment described in the foregoing, theconfiguration is made so that the positive electrode is electricallyseparated into units that can be driven separately. Thus, in addition torealizing the benefits provided by the other embodiments, it is possibleto provide a multiple wavelength light emitting device having acomparatively simple layer structure that can be easily fabricated.

Other Modifications

The present invention is not limited to or by the embodiments describedin the foregoing, but may be configured in various suitablemodifications so long as the scope of the basic concept thereof is notexceeded. The organic EL layer was used merely as representative oflight emission means, for example, and some other known light emissionmeans having a different structure may be used instead. As to the lightemission effect, moreover, optical light emission may be used inaddition to electric field light emission.

For the semi-reflecting layers, a multiple-layer dielectric film is usedin the embodiments described in the foregoing, but this is not alimitation. It is also permissible to install a thin film or opticalelement functioning as a half mirror so that the resonance conditionsare satisfied, or to use polarizing panels as the semi-reflecting layerswhile controlling the polarization.

There is also no limitation on the electronic apparatus in which themultiple wavelength light emitting device of the present invention maybe applied. It may be employed in display or illumination devices inwatches, calculators, portable telephones, pagers, electronic notebooks,notebook personal computers, and other portable information terminalapparatuses, as well as in camera viewfinders and large displays.

As based on the present invention, the configuration is made so that thewavelength output can be selected by adjusting the distance between thereflecting surface for light from the light emission means side of thesemi-reflecting layer that partially reflects light output from thelight emission region and a point existing in the interval from the endof the light emission means on the semi-reflecting layer group side tothe reflecting layer, wherefore a multiple wavelength light emittingdevice can be provided wherewith light can be ejected that is optimizedfor any of a plurality of wavelengths.

As based on the present invention, the configuration is made so that thedistance from the light emission means can be adjusted by the gapbetween the semi-reflecting layers. Therefore a multiple wavelengthlight emitting device can be provided wherewith optimization for aplurality of wavelengths is easy and which is easy to fabricate.

As based on the present invention, a multiple wavelength light emittingdevice is provided which outputs light of a plurality of optimizedwavelengths, wherefore electronic apparatuss can be provided wherein thebalance between light emission colors can be perfectly adjusted.

1. A multiple wavelength light emitting device for emitting light of aplurality of differing wavelengths comprising: light emission means foremitting light containing wavelength components to be output; areflecting layer placed in proximity to said light emission means; asemi-reflecting layer group opposite said reflecting layer with saidlight emission means therebetween, the semi-reflecting layer grouphaving semi-reflecting layers that reflect some light emitted from saidlight emission means having specific wavelengths and that transmit theremainder of the light emitted from said light emission means, stackedin order, in a direction of light advance so as to correspond with lightwavelengths to be output; and two or more light emission regions whereinthe wavelength of the output light differs wherein: the distance betweenthe reflecting layer for light from the light emission means side of thesemi-reflecting layer group that partially reflects light output fromthat light emission region and a point at which light is emitted,existing in an interval from an end surface of said light emission meanson the semi-reflecting layer group side to a surface of said reflectinglayer, is adjusted so as to have an optical path length such that lightof the wavelength output from that light emission region resonates,wherein said point in the interval from the end surface of said lightemission means on the semi-reflecting layer group side to the surface ofsaid reflecting layer is a light emission point in said light emissionmeans.
 2. A multiple wavelength light emitting device according to claim1, wherein said semi-reflecting layer group has a plurality of types ofsemi-reflecting layers responsive to light of a plurality differingwavelengths that are placed uniformly without any separation betweenlight emission regions.
 3. A multiple wavelength light emitting deviceaccording to claim 1, wherein said reflecting surface for light fromlight emission means side of semi-reflecting layer in saidsemi-reflecting layer group is in a different position in thicknessdirection for each light emission region of different light emissionwavelength.
 4. A multiple wavelength light emitting device according toclaim 1, wherein said point existing in interval from end of said lightemission means on semi-reflecting layer group side to said reflectinglayer is on reflecting surface of said reflecting layer.
 5. A multiplewavelength light emitting device according to claim 4, wherein, in alight emission region that outputs light of wavelength λ, distance Lbetween a reflecting surface for light from light emission means side ofsaid semi-reflecting layer of said plurality of semi-reflecting layersthat reflects light of wavelength λ and a point existing in intervalfrom end of said light emission means on semi-reflecting layer groupside thereof to said reflecting layer is adjusted so thatL=ΣdiΣ(ni·di)+m₁·(Φ/2π)·=m₂·λ/2 where ni is refractive index of i'thsubstance between said semi-reflecting layer and said light emittingsurface, di is thickness thereof, Φ is phase shift occurring at saidreflecting surface in said reflecting layer, and m₁ and m₂ are naturalnumbers.
 6. A multiple wavelength light emitting device according toclaim 1, wherein a point where an electric field becomes maximizedbetween electrodes in an organic electro-luminescence layer coincideswith said point at which light is emitted.
 7. A multiple wavelengthlight emitting device according to claim 1, wherein, in a light emissionregion that outputs light of wavelength λ, distance L between areflecting surface for light from light emission means side of saidsemi-reflecting layer of said plurality of semi-reflecting layers thatreflects light of wavelength λ and a light emission point existing ininterval from end of said light emission means on semi-reflecting layergroup side thereof to said reflecting layer is adjusted so thatL=ρdiΣ(ni·di)=m₂·λ/2+(2m₃+1)·λ/4 where ni is refractive index of the i'thsubstance between said reflective surface and said light emission point,di is thickness thereof, m₂ is a natural number, and m₃ is an integergreater than
 0. 8. A multiple wavelength light emitting device accordingto claim 1, wherein, in said semi-reflecting layer group, saidsemi-reflecting layer that reflects light of longer wavelength ispositioned on side nearer to said light emitting device.
 9. A multiplewavelength light emitting device according to claim 1, whereinsemi-reflecting layers configuring said semi-reflecting layer group areconfigured with two layers of different refractive index stackedalternately.
 10. A multiple wavelength light emitting device accordingto claim 9, wherein said semi-reflecting layers are adjusted so as tosatisfy the relationshipn1·d1=n2·d2=(¼+m/2)·λ where n1 is refractive index of one of said twolayers having different refractive indexes, d1 is thickness thereof, n2is refractive index of other layer, d2 is thickness thereof, λ iswavelength of light reflected in that semi-reflecting layer, and m is 0or a natural number.
 11. A multiple wavelength light emitting deviceaccording to claim 1, wherein said semi-reflecting layer group comprisesgap adjustment layers, between semi-reflecting layers thereof, foradjusting distance between reflecting surface for light from said lightemission means side of semi-reflecting layer other than thatsemi-reflecting layer closest to said light emission means and a pointexisting interval from end of said light emission means onsemi-reflecting layer group side to said reflecting layer.
 12. Amultiple wavelength light emitting device according to claim 9, wherein,in order to adjust distance between reflecting surface for light fromsaid light emission means said of semi-reflecting layer other than thatsemi-reflecting layer closest to said light emission means and a pointexisting in interval from end of said light emission means onsemi-reflecting layer group side to said reflecting layer, thickness ofone layer in laminar structure wherein said layers of differentrefractive index configure said semi-reflecting layers is altered.
 13. Amultiple wavelength light emitting device according to claim 1, whereinmultiple types of light emission means for emitting a relatively largeamount of light having light components of wavelengths corresponding tosaid light emission regions are provided so that they are associatedwith said light emission regions.
 14. A multiple wavelength lightemitting device according to claim 1, wherein light emission meanscapable of emitting light having wavelength components associated withall said light emission regions are provided commonly for all said lightemission regions.
 15. A multiple wavelength light emitting deviceaccording to claim 1, wherein said light emission means are an organicelectro-luminescence layer sandwiched between electrode layers, andelectrode provided on back side thereof corresponds to said reflectinglayer.
 16. A multiple wavelength light emitting device according toclaim 15, wherein said light emission means comprise a hole transportlayer on positive electrode side of said organic electro-luminescencelayer.
 17. A multiple wavelength light emitting device according toclaim 15, wherein said light emission means comprises an electrontransport layer on negative electrode side of said organicelectro-luminescence layer.
 18. A multiple wavelength light emittingdevice according to claim 15, wherein distance between reflectingsurface for light from light emission means side of said semi-reflectinglayers and a point existing in interval from end of said light emissionmeans on semi-reflecting layer side thereof to said reflecting layer isadjusted with thickness of positive electrode positioned onsemi-reflecting layer group side of said light emission means.
 19. Amultiple wavelength light emitting device according to claim 15,comprising a layer on semi-reflecting layer group side of said lightemission means for purpose of adjusting distance between reflectingsurface for light from light emission means side of said semi-reflectinglayers and a point existing in interval from end of said light emissionmeans on semi-reflecting layer side thereof to said reflecting layer.20. A multiple wavelength light emitting device according to claim 15,wherein said negative electrode is made of a material exhibiting lightreflectance.
 21. A multiple wavelength light emitting device accordingto claim 15, wherein at least one of electrode films sandwiched aroundsaid organic electro-luminescence layer is formed separately and isindependently, associated with said light emission regions.
 22. Amultiple wavelength light emitting device according to claim 21, whereinone or other of said electrode films is separated by a partition memberthat partitions said light emission regions from one another.
 23. Amultiple wavelength light emitting device according to claim 21,wherein, of said electrode films, the negative electrode is separated inassociation with said light emission regions, and thickness of saidpositive electrode is altered in association with said light emissionregions in order to adjust distance between reflecting surface for lightfrom light emission means side of said semi-reflecting layers and apoint existing in interval from end of said light emission means onsemi-reflecting layer side thereof to said reflecting layer.
 24. Amultiple wavelength light emitting device according to claim 21,wherein, of said electrode films, the positive electrode is separated inassociation with said light emission regions, and thickness thereof isaltered in association with said light emission regions in order toadjust distance between reflecting surface for light from light emissionmeans side of said semi-reflecting layers and a point existing ininterval from end of said light emission means on semi-reflecting layerside thereof to said reflecting layer.
 25. A multiple wavelength lightemitting device according to claim 21, comprising drive circuits forindividually driving said electrically separated electrode films.
 26. Anelectronic apparatus comprising: the multiple wavelength light emittingdevice claimed in claim
 25. 27. A electronic apparatus according toclaim 26, wherein said light emission regions in said multiplewavelength light emitting device are formed as pixels for displayingimages, and function as display elements configured so that the drivingof pixels can be controlled in response to image information.
 28. Aninterference mirror comprising: a plurality of interference reflectinglayers, configured so that some light of mutually different wavelengthcan be reflected, positioned sequentially in the direction of theoptical axis; and a plurality of gap adjacent layers, each of which hasa different thickness with respect to one another, in the direction ofthe optical axis, positioned between said interference reflectinglayers.
 29. A light emitting device, comprising: a first electrodehaving a first part and a second part; a second electrode; a lightemitting layer that is disposed between the first electrode and thesecond electrode, the light emitting layer having a first part and asecond part, the first part of the light emitting layer being disposedbetween the first part of the first electrode and the second electrode,the second part of the light emitting layer being disposed between thesecond part of the first electrode and the second electrode; asemi-reflective layer being disposed on an opposite side of the lightemitting layer with respect to the first electrode or the secondelectrode, the semi-reflective layer having a first surface thatpartially reflects the first light and a second surface that partiallyreflects the second light; a first distance between a surface of thefirst part of the first electrode that reflects a first light emitted bythe first part of the light emitting layer and the first surface of thesemi-reflective layer being adjusted such that the first lightresonates; and a second distance between a surface of the second part ofthe first electrode that reflects a second light emitted by the secondpart of the light emitting layer and the second surface of thesemi-reflective layer being adjusted such that the second lightresonates.
 30. The light emitting device according to claim 29, athickness of a first part of the second electrode being adjusted suchthat the first light resonates, and a thickness of a second part of thesecond electrode being adjusted such that the second light resonates.31. The light emitting device according to claim 29, a thickness of thefirst part of the first electrode being adjusted such that the firstlight resonates, and a thickness of the second part of the firstelectrode being adjusted such that the second light resonates.
 32. Thelight emitting device according to claim 29, further comprising: aninsulating layer that is disposed between the light emitting layer andthe second electrode, the insulating layer having a first part and asecond part, the first part of the insulating layer being disposedbetween the first part of the light emitting layer and the first part ofthe second electrode, the second part of the insulating layer beingdisposed between the second part of the light emitting layer and thesecond part of the second electrode, a thickness of the first part ofthe insulating layer being adjusted such that the first light resonates,and a thickness of the second part of the insulating layer beingadjusted such that the second light resonates.
 33. The light emittingdevice according to claim 29, each of the light emitting layer, thesecond electrode and the light emitting layer having a third part, thethird part of the light emitting layer emitting a third light, a thirdpart of the first electrode having a surface that reflects the thirdlight, and a third distance between a surface of the third part of thefirst electrode that reflects the third light and the third surface ofthe semi-reflective layer being adjusted such that the third lightresonates, wherein the semi-reflective layer further having a thirdsurface that partially reflects the third light.
 34. The light emittingdevice according to claim 29, further comprising: a hole transport layerhaving a first part and a second part, the first part of the holetransport layer being disposed between the first part of the secondelectrode and the first part of the light emitting layer, and the secondpart of the hole transport layer being disposed between the second partof the second electrode and the second part of the light emitting layer.35. The light emitting device according to claim 29, a wavelength of thefirst light being different from a wavelength of the second light. 36.The light emitting device according to claim 32, the thickness of thefirst part of the insulating layer being different from the thickness ofthe second part of the insulating layer.
 37. The light emitting deviceaccording to claim 29, the first part of the first electrode and thesecond part of the first electrode being divided from each other. 38.The light emitting device according to claim 29, a bank being providedbetween the first part of the first electrode and the second part of thefirst electrode.
 39. The light emitting device according to claim 37,further comprising: a substrate, the second electrode being disposedbetween the substrate and the light emitting layer, and the first lightand the second light being projected out from the substrate.
 40. A lightemitting device, comprising: a first electrode having a first part and asecond part; a second electrode; a light emitting layer that is disposedbetween the first electrode and the second electrode, the light emittinglayer having a first part and a second part, the first part of the lightemitting layer being disposed between the first part of the firstelectrode and the second electrode, the second part of the lightemitting layer being disposed between the second part of the firstelectrode and the second electrode; a semi-reflective layer beingdisposed on an opposite side of the light emitting layer with respect tothe first electrode or the second electrode, the semi-reflective layerhaving a first surface that partially reflects the first light and asecond surface that partially reflects the second light; a firstdistance between a surface of the first part of the first electrode thatreflects a first light emitted by the first part of the light emittinglayer and the first surface of the semi-reflective layer; and a seconddistance between a surface of the second part of the first electrodethat reflects a second light emitted by the second part of the lightemitting layer and the second surface of the semi-reflective layer, thefirst distance being different from the second distance.
 41. The lightemitting device according to claim 36, a thickness of the first part ofthe first electrode being different from a thickness of the second partof the first electrode.
 42. The light emitting device according to claim41, the first light and the second light being ejected through thesecond electrode from the light emitting device.
 43. The light emittingdevice according to claim 40, the first part of the first electrode andthe second part of the first electrode being divided from each other.44. The light emitting device according to claim 43, the first light andthe second light being projected out from the light emitting devicethrough a plurality of films.